It is known in the prior art to provide an electronic camera with variable resolution modes by which the memory capacity required for recording an image can be changed as required, for example, to cope with limited residual memory in the recording medium.
U.S. Pat. No. 5,018,017 is representative of a camera utilizing such variability in resolution modes. The problem in the prior art, as set forth in this patent, is that provision of different resolution modes complicates the compatibility of removable memory used in electronic cameras. Whereas signal processing may be simple in construction when data corresponding to each picture element is simply recorded in the removable memory, any change in the number of filter elements or the arrangement of the color filter accordingly changes the arrangement of data recorded in the memory or the amount of data per image recorded in the memory. This means that the recorded memory cannot be interchangeably used with other camera systems having different sensor arrangements. While this problem is always a serious shortcoming, it becomes even more serious, and complicated, when several resolution modes are provided because each mode is likely to be dependent upon the particular color filter arrangement in use.
U.S. Pat. No. 5,018,017 solves this problem by preprocessing the baseband image data from the sensor, in this case to form luminance and color difference signals, before providing any change in resolution. This achieves a degree of uniformity, regardless of the sensor being used. Four resolution modes are provided, a full resolution mode and a lower resolution mode obtained by subsampling the full resolution signal, and two lesser resolution modes obtained by using progressively lower quantization levels in compressing the lower resolution image. In each case, the progressively lowered resolutions are derived from a color signal that is already preconverted into a standardized form. These reduced resolution modes offer more image storage for a given memory and open the possibility of continuously photographing, and recording, a series of images in memory that would, at full resolution, only store one, or a few, images. As noted in U.S. Pat. No. 5,018,017, the upper limit of the speed attained during such a burst mode is restricted by the time required for writing into the removable memory.
The principal shortcoming of known camera systems with several resolution modes is the amount of signal processing that is done between image capture and the point at which data reduction occurs. The more processing that occurs, the more chance for noise to enter the system before the new reduced resolution image is constructed. Moreover, a principal reason for going to reduced resolution in the first place is to free up memory storage for the taking, and storage, of more pictures. The camera is then able to load as many pictures as possible, and as quickly as possible, into the camera memory. However, the camera disclosed in this patent limits the attained speed to the access time to the removable memory, a circumstance that basically does not take full advantage of the reduced resolution modes. This is particularly the case where the removable memory is, as is usually the case, the slowest memory in the system.
Consequently, an object of the invention is to collapse the processing chain between image capture and resolution reduction so that problems caused by intervening processing are avoided.
Another object is to fully utilize the collapsed processing interval for continuous photography so that a subsequent circuit element, such as the removable memory, does not appreciably limit the attainable speed.
A further object is to permit the user to select an image record size in accordance with the need, whether for continuous photography or added storage for any other reason.